1. Field of the Invention
The invention relates to modified Factor VIII (FVIII) and Factor XI (FIX) genes, nucleic acid vectors including the modified genes, optimized viral capsids including the modified genes, methods of using the modified genes in the treatment of FVIII and FIX deficiencies, such as hemophilia A and hemophilia B.
2. Discussion of Related Art
Hemophilia is a blood disorder in which the blood does not clot properly. Inadequate clotting causes excessive bleeding when the hemophiliac is injured. Hemophilia is a genetic coagulation disorder characterized by inadequate clotting and excessive bleeding. Several types of hereditary hemophilia are differentiated by the clotting factor affected. Hemophilia A is caused by a deficiency in blood coagulation Factor VIII (FVIII). Hemophilia B is caused by a deficiency in blood coagulation Factor IX (FIX).
Hemophilia B is an X-linked disorder and the condition affects ˜1 in 30 000 males. In its severe form (about 60% of the Hemophilia B population) Hemophilia B can be fatal. Spontaneous hemorrhage into joints and muscles can lead to permanent disability.
Gene therapy has been proposed as treatment modality for supplementing deficiencies in clotting factors in hemophiliacs. However, as in many areas of gene therapy, theory is much more straightforward than successful, effective application. Many difficulties have been encountered in prior attempts to engineer FVIII or FIX constructs that are suitable for treatment of humans.
For example, Manno et al. reported AAV2 mediated delivery of FIX to the liver of human subjects in a Phase I study resulted in expression of biologically active FIX levels (Manno et al., Blood, (2006), pp.). Connelly et al. reported that treatment of FVIII-deficient mice with human FVIII-encoding adenoviral vectors resulted in expression of biologically active human FVIII (Connelly et al., Blood, Vol. 91, No. 9 (1998), pp. 3273-3281). Sarker et al. reported that use of AAV8 serotype in combination with FVIII corrected plasma FVIII activity in mouse models (Sarkar et al., Blood, Vol. 103, No. 4 (2004), pp. 1253-1260).
However, as in many areas of gene therapy, theory is much more straightforward than successful, effective implementation. Difficulties in implementation of gene therapy techniques include problems encountered in the use of viruses as gene vectors. While viruses are effective as gene vectors because they can be used to transduce cells leading to protein expression in vivo, the proteins coating the virus particle may activate the body's immune system.
Thus, there is therefore a need for systems which efficiently express the target protein in sufficient quantity to reduce the required dose of viral vector to tolerable levels.